<!DOCTYPE html>
<html>
	<head>
		<meta charset="UTF-8">
		<title></title>
	</head>
	<body>
	</body>
	<script type="text/javascript">
		var obj={
			
		};
		Object.defineProperty(obj,"age",{
			value:18,
//			writable:false,
//			configurable:false,
//			enumerable:true
		})
		Object.defineProperty(obj,"age",{
			value:18,
			writable:true,
		})
		
		
		obj.age=30;
		console.log(obj.age);
	
		//不会出现在for in中
		for(item in obj){
			console.log(item);
		}
	</script>
</html>
